Water cooling wall safety monitoring method and combustion adjustment control method based on distributed optical fiber sensing

Abstract

The invention provides a water-cooled wall safety monitoring method and a combustion adjustment control method based on distributed optical fiber sensing, and the method specifically comprises the following steps: arranging a Bragg grating on a water-cooled wall, and obtaining the Bragg wavelength offset; predicting a temperature value and a strain value at the current moment according to historical temperature and strain data by using a state equation of stress and temperature; the Bragg wavelength prediction offset is obtained by combining the temperature value and the strain value at the current moment with the sensor error; obtaining a wavelength change residual error according to the Bragg wavelength offset and the Bragg wavelength prediction offset, and correcting the temperature value and the strain value at the current moment by using the wavelength change residual error to obtain a real temperature value and a real strain value at the current moment; a real strain value at the current moment is converted into a stress value, a water-cooled wall tearing factor is established by utilizing the stress value, the number of thermal cycles and the fatigue life of a water-cooled wall material, water-cooled wall safety monitoring and combustion adjustment control are realized by utilizing the water-cooled wall tearing factor, and the operation safety of the boiler is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of intelligent boiler monitoring and control, and specifically belongs to a water wall safety monitoring method and a combustion adjustment control method based on distributed optical fiber sensing for furnace stress monitoring and intelligent operation optimization in thermal power plants. Background Art

[0002] When the water wall is repeatedly heated and expanded or cooled and contracted at high temperatures, it is easy to cause plastic deformation at the stress concentration position, thinning and deforming the water wall pipe wall or even bursting the pipe. The abnormal stress of the water wall will be transmitted to the boiler steel frame through the rigid hanger, causing secondary problems such as tearing of the expansion joint and failure of the furnace top seal. At present, the on-line monitoring means for the stress of the water wall are relatively weak. Usually, multiple strain gauges are arranged on the outer wall surface of the water wall, and the stress of the water wall is calculated through Hooke's law of elastic deformation on the wall surface. The coverage range of its device is small, the strain distribution of the water wall cannot be obtained, and the monitoring effect on the stress concentration part with a small size is limited. In addition, the current technology does not further process the stress monitoring results of the water wall, and the stress monitoring results cannot provide actual guidance and optimization suggestions for boiler operation. Summary of the Invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a water wall safety monitoring method and a combustion adjustment control method based on distributed optical fiber sensing. By using the distributed optical fiber sensing technology, the strain and temperature changes of the water wall are accurately captured through Bragg gratings, and the tearing factor of the water wall is defined to quantify the safety factor, so as to realize the safety monitoring of the water wall. In addition, a stress-combustion coupling closed-loop intelligent control mechanism is constructed, and the combustion parameters are optimized in real time through the boiler bias combustion index, realizing a full-process closed loop of "real-time monitoring → stress anomaly identification → combustion optimization adjustment → intelligent control", and improving the safety and stability of boiler operation.

[0004] To achieve the above object, the present invention provides the following technical solution: A water wall safety monitoring method based on distributed optical fiber sensing, the specific steps are as follows: Arrange Bragg gratings on the water wall to obtain the Bragg wavelength shift; Using the state equation of stress and temperature, predict the temperature value and strain value at the current moment according to historical temperature and strain data; Obtain the predicted Bragg wavelength shift by combining the temperature value and strain value at the current moment with the sensor error; Obtain the wavelength change residual according to the Bragg wavelength shift and the predicted Bragg wavelength shift, and use the wavelength change residual to correct the temperature value and strain value at the current moment to obtain the true temperature value and strain value at the current moment; Convert the true strain value at the current moment into a stress value, and establish a water wall tearing factor using the stress value, the number of thermal cycles, and the fatigue life of the water wall material. The water wall tearing factor is used as an evaluation index for the safe operation of the water wall to achieve the safety monitoring of the water wall.

[0005] Furthermore, after the Bragg grating is protected and encapsulated, it is arranged in a spiral winding manner along the height direction of the boiler water wall tube screen. Three groups of Bragg gratings are arranged on each water wall tube on the front wall, side wall, and rear wall respectively, and the adjacent spacing is controlled within 100 mm; an optical demodulator is used to analyze the reflection spectrum of the Bragg grating to obtain the Bragg wavelength shift.

[0006] Furthermore, the Bragg wavelength shift is calculated as follows:

[0007] In the formula, is the Bragg wavelength shift; is the strain sensitivity coefficient; is the temperature sensitivity coefficient; Higher-order nonlinear coupling terms; Higher-order nonlinear coupling terms are expressed as follows:

[0008] In the formula, is the strain, T is the temperature, a 1 , a 2 , a 3 are the coupling term coefficients of the water wall pipe material, which are determined through calibration tests.

[0009] Furthermore, the state equation of the stress and temperature is:

[0010] In the formula, is the strain value at the current moment; T k is the temperature value at the current moment; is the strain value at the previous moment; T k-1 is the temperature value at the previous moment; and are the strain error and temperature error respectively; is the theoretical temperature rise calculated from the heat flux density; During the start-up and shutdown stages of the boiler, obtain the initial boiler stress = 0 and the temperature T at the position of the boiler water wall 0, and taking this moment as the initial state of the boiler, the temperature value and strain value at the current moment are predicted by dynamically recursively solving the state equation.

[0011] Furthermore, the predicted offset of the Bragg wavelength is calculated as follows:

[0012] In the formula, z k is the offset of the Bragg wavelength; is the strain sensitivity coefficient; is the temperature sensitivity coefficient; is the high-order nonlinear coupling term; v k is the measurement system error of the sensor itself; high-order nonlinear coupling term is expressed as follows:

[0013] In the formula, is the strain, T is the temperature, a 1 , a 2 , a 3 are the coupling term coefficients of the water wall pipe material, which are determined by calibration tests.

[0014] Furthermore, the true temperature value and strain value at the current moment are calculated as follows:

[0015] In the formula, T e and respectively represent the true temperature value and strain value at the current moment, is the strain sensitivity coefficient; is the temperature sensitivity coefficient, is the strain value at the current moment; T k is the temperature value at the current moment; is the offset of the Bragg wavelength; z k is the offset of the Bragg wavelength; Taking the true temperature value and strain value at the current moment as the initial state of the temperature and strain data at the previous moment, the true temperature value and strain value at the next current moment are predicted using the state equation of stress and temperature.

[0016] Furthermore, the water wall tearing factor F is calculated as follows:

[0017] In the formula, is the yield stress of the water wall material; N is the number of thermal cycles, which can be determined by the wall temperature fluctuation period; N f is the fatigue life of the water wall material;

[0018] In the formula, is the stress, E is the elastic modulus, is the true strain value at the current moment; When F ≤ 0.5, the water wall is safe without risk; When 0.5 < F < 0.9, the water wall has medium safety risk; When F ≥ 0.9, the water wall has high safety risk.

[0019] The present invention also provides a combustion adjustment control method based on the stress change of the water wall. The boiler uneven combustion index is calculated according to the boiler steam temperature deviation, flue gas temperature deviation and water wall tearing factor. When the boiler uneven combustion index is higher than the set value, the boiler operation data is adjusted according to the combustion optimization operation law; wherein the water wall tearing factor is obtained from the above-mentioned water wall safety monitoring method based on distributed optical fiber sensing.

[0020] Furthermore, the boiler uneven combustion index is calculated as follows:

[0021] In the formula, F is the water wall tearing factor, is the boiler steam temperature deviation, is the flue gas temperature deviation, a 1 , a 2 , a 3 is the weight coefficient.

[0022] Furthermore, the boiler operation data includes the opening of the secondary air damper, the oxygen content and the coal feeding amount of the coal mill, and the actuators are the secondary air fan, the variable frequency damper and the hydraulic regulating valve of the coal feeder.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a method for safety monitoring of a water wall based on distributed optical fiber sensing. 1) Using a Bragg grating as a sensing element, it has the characteristics of distributed measurement and can capture the strain and temperature changes at various positions of the water wall, providing a rich data basis for accurately evaluating the safety state of the water wall. 2) Utilizing the state equation of stress and temperature to predict the temperature value and strain value at the current moment, and continuously iteratively updating the prediction values. This dynamic monitoring method can track the state changes of the water wall in real time, and by continuously correcting the prediction values, it improves the real-time performance and accuracy of the monitoring. 3) Defining the water wall tearing factor as an evaluation index for the safety of the water wall, comprehensively considering factors such as the yield stress of the water wall material, the number of thermal cycles, and the fatigue life of the water wall material. By calculating the water wall tearing factor F, the safety factor of the water wall can be quantified, intuitively reflecting the safety state of the water wall. The method of the present invention considering multiple factors comprehensively can more accurately reflect the actual safety condition of the water wall, avoiding the limitations of single-factor evaluation, and the evaluation results are more comprehensive and reliable.

[0024] Compared with traditional strain gauge sensors, the Bragg grating can be arranged in a spiral winding manner along the height direction of the water wall tube panel. Three groups are arranged on each water wall tube at the front wall, side wall, and rear wall respectively, and the adjacent spacing is controlled within 100 mm, realizing comprehensive and detailed monitoring of the strain and temperature of the water wall. Solving the problem that traditional strain gauge sensors cannot capture the two-dimensional stress distribution of the water wall, using a material calibration test to determine the strain and temperature nonlinear coupling coefficient of the Bragg grating, eliminating the temperature-strain cross-sensitivity error, and improving the strain measurement accuracy. The central wavelength of the Bragg grating is 1550 nm, the grating region length is 10 mm, and the temperature resistance level is not lower than 600 degrees Celsius, which can adapt to the harsh working environment of high temperature and high pressure of the boiler water wall. The characteristics of its reflection spectrum enable the precise analysis of the Bragg wavelength shift amount through an optoelectronic demodulator, and then calculate the strain and temperature changes.

[0025] In actual measurement, the changes in temperature and strain will both cause the shift of the Bragg grating reflection wavelength, resulting in the problem of temperature-strain cross-sensitivity. This method determines the coupling term coefficient of the water wall tube material through a material calibration test, and introduces a high-order nonlinear coupling term into the calculation formula, thereby eliminating the temperature-strain cross-sensitivity error. This makes the measurement results of strain and temperature more accurate and reliable, and improves the monitoring accuracy.

[0026] Set up a three - level safety warning mechanism. When F ≤ 0.5, the water - cooled wall is safe without risk; when 0.5 < F < 0.9, the water - cooled wall has medium safety risk; when F ≥ 0.9, the water - cooled wall has high safety risk. When medium and high risks occur, the DCS gives an alarm and starts the interlock protection program. When necessary, the problem of water - cooled wall tearing is controlled by load shedding. This warning mechanism can timely detect the safety risks of the water - cooled wall and take corresponding measures to ensure the safe operation of the boiler.

[0027] The present invention also provides a combustion adjustment control method based on the stress change of the water - cooled wall. Using the water - cooled wall tearing factor obtained by the water - cooled wall safety monitoring method based on distributed optical fiber sensing, combined with factors such as boiler steam temperature deviation and flue gas temperature deviation, the boiler uneven combustion index is calculated. The boiler uneven combustion index can comprehensively reflect the uniformity and stability of boiler combustion, providing an accurate basis for combustion adjustment. This method constructs a closed - loop intelligent control mechanism of stress - combustion coupling, and the boiler uneven combustion index realizes real - time optimization adjustment of boiler combustion. When the boiler uneven combustion index is higher than the set value, the boiler operation data is adjusted according to the combustion optimization operation rules, such as the opening of secondary air dampers, oxygen content, and coal feeding amount of coal mills. This closed - loop control mechanism can adjust combustion parameters in real time according to the changes of water - cooled wall stress and combustion state, making the boiler always in the best operation state. Through continuous feedback and adjustment, the combustion efficiency and stability of the boiler are improved, and pollutant emissions are reduced.

[0028] The method of the present invention establishes a full - process closed - loop control system of "real - time monitoring → stress anomaly identification → combustion optimization adjustment → intelligent control". Starting from real - time monitoring of the water - cooled wall stress and combustion state, to identifying stress anomalies and uneven combustion phenomena, then to adjusting combustion according to the optimization rules, and finally realizing intelligent control, a complete control process is formed. This full - process closed - loop control can timely detect and solve problems occurring during the operation of the boiler, ensuring the safe and stable operation of the boiler. Through real - time monitoring and feedback adjustment, the operation efficiency and safety of the boiler can be continuously improved, and equipment damage and shutdown accidents caused by combustion problems can be reduced. Brief Description of the Drawings

[0029] Figure 1 It is a flow chart of the stress dynamic recursive solution algorithm. Detailed Embodiments

[0030] The following further describes the present invention in conjunction with the drawings and specific embodiments.

[0031] The present invention provides a water - cooled wall safety monitoring method based on distributed optical fiber sensing, and the specific steps are as follows: (1) Arrange a water - cooled wall stress distribution monitoring system on the water - cooled wall to obtain the wavelength shift of the Bragg grating; (2)Establish a decoupling algorithm for the temperature and strain of the fiber Bragg grating to obtain the on-line strain value of the water-cooled wall; (3)Construct a stress warning model for the water-cooled wall to obtain the tearing factor of the water-cooled wall, and obtain the prediction result of the safety of the water-cooled wall based on the tearing factor of the water-cooled wall; Step (1) includes the following sub-steps: S1: The hardware of the slagging distribution and stress distribution on-line monitoring system includes: temperature measuring elements, fiber Bragg gratings, wavelength division multiplexers, data receivers and laser light sources. The fiber Bragg gratings are arranged along the outer wall surface of the water-cooled wall after being protected and packaged. The central wavelength of the fiber Bragg grating is 1550 nm, the grating area length is 10 mm, and the temperature resistance level is not less than 600 degrees Celsius. The fiber Bragg gratings are arranged in a spiral winding manner along the height direction of the boiler water-cooled wall tube screen. Three groups of fiber Bragg gratings are arranged on each water-cooled wall tube on the front wall, side wall and rear wall respectively, and the distance between adjacent fiber Bragg gratings is controlled within 100 mm.

[0032] S2: The data receiver uses an optoelectronic demodulator, and the goal is to analyze the reflection spectrum wavelength offset of the fiber Bragg grating. The relationship between the reflection light wavelength offset of the fiber Bragg grating and strain and temperature T is shown in the following formula: (1) In the formula, is the Bragg wavelength offset; is the strain sensitivity coefficient; is the temperature sensitivity coefficient; is the high-order nonlinear coupling term.

[0033] S3: The coupling term coefficients a 1 , a 2 , a 3 of the water-cooled wall pipe material can be determined through a calibration test. For the common material SA210C of the water-cooled wall, can be expressed as: (2) In the formula, a 1 takes 4.6×10 -3 , a 2 takes 2.3×10 -4 , a 3 takes 9.2×10 -5 .

[0034] Step (2) includes the following sub-steps: S1: To eliminate the coupling of temperature changes to strain measurement, a dynamic recursive solution algorithm is adopted. The state equations for stress and temperature are as follows: (3) In the formula, is the strain value at the current moment; T k is the temperature value at the current moment; is the strain value at the previous moment; T k-1 is the temperature value at the previous moment; and are the strain error and temperature error respectively; is the theoretical temperature rise calculated from the heat flux density.

[0035] During the start-up and shutdown stages of the boiler, the initial boiler stress = 0 and the temperature T at the position of the boiler water wall 0 are obtained, and this moment is taken as the initial state of the boiler.

[0036] According to the principle of the wavelength change of the Bragg grating, an observation equation is established to obtain the predicted offset of the Bragg wavelength z k : (4) In the formula, v k is the measurement system error of the sensor itself. The system relative error is related to the equipment used and is generally less than 3%.

[0037] S2: Predict the temperature T k and strain at the current moment according to historical data, and substitute them into the observation equation (Formula 4). and are the strain error and temperature error respectively, and the error takes plus or minus 3%. Calculate the predicted value z k of the wavelength change.

[0038] S3: Read the actual wavelength change of the device, calculate the wavelength change residual. The larger the residual, the greater the deviation between the predicted value and the actual value. According to the following correction formula, obtain the temperature and strain correction values: (5) In the formula, T e and represent the actual temperature value and strain value at the current moment respectively. And take this actual value as the initial state of the next moment and substitute it into Formula (3) for continuous iterative update.

[0039] Step (3) includes the following sub-steps: S1: Calculate the stress according to Hooke's law , and the elastic modulus of the water wall can be obtained in advance through experiments; Hooke's law is specifically: (6) In the formula, is the stress, E is the elastic modulus, is the true strain value at the current moment.

[0040] S2: Define the water wall tearing factor F as the evaluation index for the safe operation of the water wall: (7) In the formula, is the yield stress of the water wall material; N is the number of thermal cycles, which can be determined by the wall temperature fluctuation period; N f is the fatigue life of the water wall material.

[0041] Set three-level safety warnings for the water wall: When F ≤ 0.5, the water wall is safe without risk, and a green signal is displayed on the DCS; When 0.5 < F < 0.9, the water wall triggers a secondary safety warning, the water wall has a medium safety risk, a yellow warning signal is displayed on the DCS screen, and the interlock protection program is started; When F ≥ 0.9, the water wall triggers a primary safety warning, the water wall has a high safety risk, a red warning signal is displayed on the DCS screen, the interlock protection program is started, and the tearing problem of the water wall is controlled by load shedding when necessary.

[0042] Based on the above water wall safety monitoring method based on distributed optical fiber sensing, a combustion adjustment control method based on the stress change of the water wall is proposed. This control method is based on the monitoring results, constructs a combustion deviation identification mechanism model, and based on the historical and real-time economic and environmental protection data of the power plant, obtains the optimal values of parameters such as secondary air damper, oxygen content, and coal quantity distribution of the coal mill based on an optimization intelligent algorithm, and performs closed-loop optimization control, specifically as follows: S1: Combine the water wall tearing factor F , the steam temperature deviation of the boiler ΔT s , and the flue gas temperature deviation ΔT y to establish a boiler combustion and water wall stress function model to calculate the boiler combustion deviation index. This function model considers the stress distribution uniformity of the four-sided water wall of the boiler and can intelligently identify combustion deviation. The boiler combustion deviation index It is expressed as follows: (8) In the formula, a 1 , a 2 , a 3 are weight coefficients, a 1 , a 2 , a 3 The weight distribution ratio of is 3:2:1.

[0043] S2: According to the result of the recognition objective function, based on the optimization algorithm, intelligent optimization adjustment is carried out on the secondary air damper opening, oxygen content and coal feeding amount of the coal mill. The actuators are mainly the secondary air fan, variable frequency damper and hydraulic regulating valve of the coal feeder.

[0044] S3: Real-time communication of equipment is carried out through the modbus TCP / IP protocol. The data frame format is 32-bit floating-point number, and the transmission period ≤ 100 ms. The intelligent adjustment result is transmitted to the on-site equipment to achieve intelligent control. The total response time of intelligent recognition, adjustment and control is less than 10 s.

[0045] Example 1 The combustion adjustment control method based on the stress change of the water wall proposed by the present invention is actually applied and verified on a certain 330MW subcritical coal-fired boiler unit. The boiler adopts a П-type layout, the water wall tube screen is made of SA210C, the furnace height is 68 meters, and 120 vertical tubes are arranged on each of the front and rear walls. To implement the method of the present invention, a distributed optical fiber sensing network is first deployed in the key areas of the water wall.

[0046] Along the outer wall surfaces of the water walls on the front wall, two side walls and the rear wall of the boiler, high-temperature resistant fiber Bragg grating sensors are arranged in a spiral winding manner. A set of sensing units is set every 200 mm in the height direction of each tube, the central wavelength is set to 1550 ± 0.2 nm, the grating area length is 10 mm, and it is encapsulated with an alumina ceramic protective sleeve, and the temperature resistance level reaches 800 °C. The data acquisition system uses a 16-channel optoelectronic demodulator, the sampling frequency is set to 10 Hz, and the signal is transmitted to the upper computer in the control room through armored optical cables. Select SA-210C samples to complete the initial calibration and obtain the elastic modulus of SA-210C pipe material E = 195 GPa, yield strength σ max = 325 MPa, fatigue life Nf = 3×10 5 times.

[0047] After the system is put into operation, the wavelength shift is collected in real timeΔλ Data flow. When the boiler load rises to 75% BMCR, a certain sensor in the middle of the front wall measures Δλ = 0.85 nm. Establish the state equation according to formula (3), and initially set ε 0 = 0, T 0 = 320 °C. Back-calculate the theoretical temperature rise through the heat flux density ΔTq = 8 °C / min. According to the Figure 1 process calculation, after 500 iterations, the true strain ε e = 0.12% and the actual temperature T e = 368 °C are separated and substituted into formula (7) to obtain F = 0.67.

[0048] The set value of the boiler uneven combustion index is 1.5. When the stress deviation between the left and right side walls exceeds 10%, it reaches the combustion skewness threshold. Combining the steam temperature deviation ΔT s = 12 °C and the flue gas temperature deviation ΔT y = 25 °C, calculate the boiler uneven combustion index according to formula (8) f(x) = 3×0.67 + 2×0.12 + 1×0.25 = 2.38. Compared with the set value, the boiler uneven combustion index is relatively high. According to the combustion optimization operation law, reduce the opening of the secondary air damper on the side with higher stress by 5% and the coal quantity distribution of the coal mill by 5%, and increase the opening of the secondary air damper on the side with lower stress by 5% and the coal quantity distribution of the coal mill by 5%. The adjustment instruction is sent through the Modbus TCP / IP protocol, and the 32-bit floating-point data frame is transmitted through the redundant optical fiber ring network, and the full-process response time is 7.8 seconds. The stress difference of the water wall is reduced to less than 3%, and the absolute value of the steam temperature deviation on both sides is maintained within 5°.

[0049] During the three-month continuous operation of the system, the combustion optimization improves the boiler efficiency by 0.45%. This embodiment proves that the present invention realizes a complete closed-loop from stress monitoring to combustion control, significantly improving the operation safety and economy of the boiler.

[0050] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For a person skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced by the present invention. Any reference signs in the claims should not be construed as limiting the claims concerned.

[0051] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment only contains an independent technical solution. This narrative style of the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in the various embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any modification made on the basis of the technical solution according to the technical idea proposed by the present invention falls within the protection scope of the claims of the present invention.

Claims

1. A water-cooled wall safety monitoring method based on distributed optical fiber sensing, characterized in that: The specific steps are as follows: Arrange a Bragg grating on the water-cooled wall to obtain the Bragg wavelength shift; Using the state equation of stress and temperature, based on historical temperature and strain data, the temperature and strain values ​​at the current moment are predicted; The predicted Bragg wavelength offset is obtained by combining the temperature value and strain value at the current moment with the sensor error; The wavelength change residual is obtained according to the Bragg wavelength offset and the Bragg wavelength prediction offset, and the temperature value and strain value at the current moment are corrected by using the wavelength change residual to obtain the real temperature value and strain value at the current moment; The real strain value at the current moment is converted into a stress value, and the water-cooled wall tearing factor is established using the stress value, the number of thermal cycles and the fatigue life of the water-cooled wall material. The water-cooled wall tearing factor is used as a water-cooled wall safety evaluation indicator to realize water-cooled wall safety monitoring.

2. The water-cooled wall safety monitoring method based on distributed optical fiber sensing according to claim 1 is characterized in that: After being protected and packaged, the Bragg grating is laid out in a spiral winding manner along the height direction of the boiler water-cooled wall tube panel. Three groups of Bragg gratings are arranged on the front wall, side wall and rear wall of each water-cooled wall tube, and the adjacent spacing is controlled within 100mm. The Bragg grating reflection spectrum is analyzed by a photoelectric demodulator to obtain the Bragg wavelength offset.

3. The water-cooled wall safety monitoring method based on distributed optical fiber sensing according to claim 2 is characterized in that: The Bragg wavelength shift is calculated as follows: In the formula, is the Bragg wavelength shift; is the strain sensitivity coefficient; is the temperature sensitivity coefficient; High-order nonlinear coupling terms; High-order nonlinear coupling terms It is expressed as follows: In the formula, For strain, T is the temperature, a 1. a 2. a 3 is the coupling coefficient of the water-cooled wall tube material, which is determined through calibration tests.

4. The water-cooled wall safety monitoring method based on distributed optical fiber sensing according to claim 1 is characterized in that: The state equation of stress and temperature is: In the formula, is the strain value at the current moment; T k is the temperature value at the current moment; is the strain value at the previous moment; T k-1 is the temperature value at the previous moment; and are strain error and temperature error respectively; is the theoretical temperature rise calculated from the heat flux; During the start-up and shutdown phases of the boiler, the initial boiler stress =0 and the boiler water wall position temperature T0, and take this moment as the boiler initial state, and use dynamic recursion to solve the state equation to predict the temperature value and strain value at the current moment.

5. The water-cooled wall safety monitoring method based on distributed optical fiber sensing according to claim 1 is characterized in that: The predicted shift in Bragg wavelength is calculated as follows: In the formula, z k is the Bragg wavelength shift; is the strain sensitivity coefficient; is the temperature sensitivity coefficient; High-order nonlinear coupling terms; v k Measuring system error for the sensor itself; High-order nonlinear coupling terms It is expressed as follows: In the formula, For strain, T is the temperature, a 1. a 2. a 3 is the coupling coefficient of the water-cooled wall tube material, which is determined through calibration tests.

6. The water-cooled wall safety monitoring method based on distributed optical fiber sensing according to claim 1 is characterized in that: The actual temperature and strain values ​​at the current moment are calculated as follows: In the formula, T e and Respectively represent the actual temperature value and strain value at the current moment, is the strain sensitivity coefficient; is the temperature sensitivity coefficient, is the strain value at the current moment; T k is the temperature value at the current moment; is the Bragg wavelength shift; z k is the Bragg wavelength shift; The actual temperature and strain values ​​at the current moment are taken as the initial state of the temperature and strain data at the previous moment, and the state equation of stress and temperature is used to predict the actual temperature and strain values ​​at the next current moment.

7. The water-cooled wall safety monitoring method based on distributed optical fiber sensing according to claim 1 is characterized in that: Water wall tearing factor F The calculation is as follows: In the formula, is the yield stress of water wall material; N is the number of thermal cycles, which can be determined by the wall temperature fluctuation period; N f is the fatigue life of the water wall material; In the formula, is stress, E is the elastic modulus, is the actual strain value at the current moment; When F≤0.5, the water-cooled wall is safe and risk-free; When F>0.5 and F<0.9, the water wall safety risk is medium; When F ≥ 0.9, the water-cooled wall safety is at high risk.

8. A combustion adjustment control method based on water-cooled wall stress change, characterized in that: The boiler bias burning index is calculated based on the boiler air temperature deviation, smoke temperature deviation and water wall tearing factor. When the boiler bias burning index is higher than the set value, the boiler operation data is adjusted according to the combustion optimization operation law; The water-cooled wall tearing factor is obtained from a water-cooled wall safety monitoring method based on distributed optical fiber sensing according to any one of claims 1 to 7.

9. The combustion adjustment control method based on water wall stress change according to claim 8, characterized in that: Boiler bias index The calculation is as follows: In the formula, F is the water wall tearing factor, is the boiler air temperature deviation, is the smoke temperature deviation, a 1, a 2, a 3 is the weight coefficient.

10. The combustion adjustment control method based on water wall stress change according to claim 8, characterized in that: The boiler operation data includes the secondary air door opening, oxygen content and coal feed rate of the pulverizer. The actuators are the secondary fan, variable frequency air door and hydraulic regulating valve of the coal feeder.

Images